Electric double layer capacitors are generally excellent in charge-discharge characteristics.
FIG. 17 is a sectional view of a cell 2 of a conventional electric double layer capacitor 1 (see Japanese Unexamined Patent Publication No. 2001-351833). The cell includes a pair of polarizable electrodes 20, 21 stacked with the intervention of a separator 6, and collector electrodes 3, 30 of a metal are respectively attached to outer sides of the polarizable electrodes 20, 21. The polarizable electrodes 20, 21 are prepared by adding an electrically conductive polymer such as polypyrrole to powdery or fibrous active carbon, and compacting and press-molding the active carbon together with a binder. The polarizable electrodes 20, 21 are each impregnated with an electrolytic solution such as of sulfuric acid. Not only an aqueous solution such as the sulfuric acid solution but also a nonaqueous solution to be described later is usable as the electrolytic solution.
Peripheral portions of the polarizable electrodes 20, 21 are sealed with an insulative sealing member 4 of a synthetic resin. The sealing member 4 prevents the electrolytic solution from leaking out of the cell 2. In general, one or more such cells 2 are arranged laterally to constitute the electric double layer capacitor 1.
When the cell is charged, a DC voltage is applied between the collector electrodes with one of the collector electrodes 3 being connected to a positive terminal of a power source and with the other collector electrode 30 being connected to a negative terminal of the power source. Anions are attracted to the polarizable electrode 20 connected to the positive collector electrode 3, and cations are attracted to the polarizable electrode 21 connected to the negative collector electrode 30. Thus, an electric double layer structure is formed by the polarizable electrodes 3, 30.
When the cell is discharged, the collector electrodes 3, 30 are electrically connected to each other. Thus, electric charges accumulated in the polarizable electrodes 20, 21 are discharged.
In the electric double layer capacitor, however, the adhesion between the collector electrodes 3, 30 and the sealing member 4 is poor. Therefore, the electrolytic solution impregnated in the polarizable electrodes 20, 21 is liable to leak from gaps between the collector electrodes 3, 30 and the sealing member 4, or moisture is liable to intrude into the inside of the sealing member 4 from the outside of the cell 2.
Particularly, the nonaqueous electrolytic solution is liable to be electrolyzed in the cell 2 due to the intrusion of the moisture from the outside, thereby deteriorating the characteristic properties of the electric double layer capacitor.
It is an object of the present invention to provide an electric double layer capacitor and an electrolytic battery which are free from the leakage of the electrolytic solution and the intrusion of the moisture from the outside.